add DynamicRole

Signed-off-by: Yaliang Wu <ylwu@amazon.com>

server/src/main/java/org/opensearch/cluster/node/DiscoveryNode.java

@@ -328,7 +328,11 @@ public DiscoveryNode(StreamInput in) throws IOException {
                 }
                 final DiscoveryNodeRole role = roleMap.get(roleName);
                 if (role == null) {
-                    roles.add(new DiscoveryNodeRole.UnknownRole(roleName, roleNameAbbreviation, canContainData));
+                    if (in.getVersion().onOrAfter(Version.V_2_1_0)) {
+                        roles.add(new DiscoveryNodeRole.DynamicRole(roleName, roleNameAbbreviation, canContainData));
+                    } else {
+                        roles.add(new DiscoveryNodeRole.UnknownRole(roleName, roleNameAbbreviation, canContainData));
+                    }
                 } else {
                     assert roleName.equals(role.roleName()) : "role name [" + roleName + "] does not match role [" + role.roleName() + "]";
                     assert roleNameAbbreviation.equals(role.roleNameAbbreviation()) : "role name abbreviation ["
@@ -570,7 +574,7 @@ public static DiscoveryNodeRole getRoleFromRoleName(final String roleName) {
         if (roleMap.containsKey(roleName)) {
             return roleMap.get(roleName);
         }
-        return new DiscoveryNodeRole.UnknownRole(roleName, roleName, false);
+        return new DiscoveryNodeRole.DynamicRole(roleName, roleName, false);
     }
 
     public static Set<DiscoveryNodeRole> getPossibleRoles() {

server/src/main/java/org/opensearch/cluster/node/DiscoveryNodeRole.java

@@ -94,13 +94,19 @@ public final boolean canContainData() {
 
     private final boolean isKnownRole;
 
+    private final boolean isDynamicRole;
+
     /**
      * Whether this role is known by this node, or is an {@link DiscoveryNodeRole.UnknownRole}.
      */
     public final boolean isKnownRole() {
         return isKnownRole;
     }
 
+    public final boolean isDynamicRole() {
+        return isDynamicRole;
+    }
+
     public boolean isEnabledByDefault(final Settings settings) {
         return legacySetting() != null && legacySetting().get(settings);
     }
@@ -110,16 +116,18 @@ protected DiscoveryNodeRole(final String roleName, final String roleNameAbbrevia
     }
 
     protected DiscoveryNodeRole(final String roleName, final String roleNameAbbreviation, final boolean canContainData) {
-        this(true, roleName, roleNameAbbreviation, canContainData);
+        this(true, false, roleName, roleNameAbbreviation, canContainData);
     }
 
     private DiscoveryNodeRole(
         final boolean isKnownRole,
+        final boolean isDynamicRole,
         final String roleName,
         final String roleNameAbbreviation,
         final boolean canContainData
     ) {
         this.isKnownRole = isKnownRole;
+        this.isDynamicRole = isDynamicRole;
         this.roleName = Objects.requireNonNull(roleName);
         this.roleNameAbbreviation = Objects.requireNonNull(roleNameAbbreviation);
         this.canContainData = canContainData;
@@ -152,12 +160,13 @@ public final boolean equals(Object o) {
         return roleName.equals(that.roleName)
             && roleNameAbbreviation.equals(that.roleNameAbbreviation)
             && canContainData == that.canContainData
-            && isKnownRole == that.isKnownRole;
+            && isKnownRole == that.isKnownRole
+            && isDynamicRole == that.isDynamicRole;
     }
 
     @Override
     public final int hashCode() {
-        return Objects.hash(isKnownRole, roleName(), roleNameAbbreviation(), canContainData());
+        return Objects.hash(isKnownRole, isDynamicRole, roleName(), roleNameAbbreviation(), canContainData());
     }
 
     @Override
@@ -177,6 +186,7 @@ public final String toString() {
             + ", canContainData="
             + canContainData
             + (isKnownRole ? "" : ", isKnownRole=false")
+            + (isDynamicRole ? "" : ", isDynamicRole=false")
             + '}';
     }
 
@@ -298,7 +308,7 @@ public Setting<Boolean> legacySetting() {
 
     /**
      * Represents an unknown role. This can occur if a newer version adds a role that an older version does not know about, or a newer
-     * version removes a role that an older version knows about, or some custom role for extension function provided by plugin.
+     * version removes a role that an older version knows about.
      */
     static class UnknownRole extends DiscoveryNodeRole {
 
@@ -310,7 +320,7 @@ static class UnknownRole extends DiscoveryNodeRole {
          * @param canContainData       whether or not nodes with the role can contain data
          */
         UnknownRole(final String roleName, final String roleNameAbbreviation, final boolean canContainData) {
-            super(false, roleName, roleNameAbbreviation, canContainData);
+            super(false, false, roleName, roleNameAbbreviation, canContainData);
         }
 
         @Override
@@ -322,6 +332,32 @@ public Setting<Boolean> legacySetting() {
 
     }
 
+    /**
+     * Represents a dynamic role. This can occur if a custom role that not in {@link DiscoveryNodeRole#BUILT_IN_ROLES} added for a node.
+     * Some plugin can support extension function with dynamic roles. For example, ML plugin may run machine learning tasks on nodes
+     * with "ml" dynamic role.
+     */
+    static class DynamicRole extends DiscoveryNodeRole {
+
+        /**
+         * Construct a dynamic role with the specified role name and role name abbreviation.
+         *
+         * @param roleName             the role name
+         * @param roleNameAbbreviation the role name abbreviation
+         * @param canContainData       whether or not nodes with the role can contain data
+         */
+        public DynamicRole(final String roleName, final String roleNameAbbreviation, final boolean canContainData) {
+            super(false, true, roleName, roleNameAbbreviation, canContainData);
+        }
+
+        @Override
+        public Setting<Boolean> legacySetting() {
+            // return null as dynamic role has no legacy setting
+            return null;
+        }
+
+    }
+
     /**
      * Check if the role is {@link #CLUSTER_MANAGER_ROLE} or {@link #MASTER_ROLE}.
      * @deprecated As of 2.0, because promoting inclusive language. MASTER_ROLE is deprecated.

server/src/test/java/org/opensearch/cluster/node/DiscoveryNodeRoleTests.java

@@ -117,7 +117,7 @@ public void testDiscoveryNodeRoleEqualsHashCode() {
 
     }
 
-    public void testUnknownRoleIsDistinctFromKnownRoles() {
+    public void testUnknownRoleIsDistinctFromKnownOrDynamicRoles() {
         for (DiscoveryNodeRole buildInRole : DiscoveryNodeRole.BUILT_IN_ROLES) {
             final DiscoveryNodeRole.UnknownRole unknownDataRole = new DiscoveryNodeRole.UnknownRole(
                 buildInRole.roleName(),
@@ -126,6 +126,15 @@ public void testUnknownRoleIsDistinctFromKnownRoles() {
             );
             assertNotEquals(buildInRole, unknownDataRole);
             assertNotEquals(buildInRole.toString(), unknownDataRole.toString());
+            final DiscoveryNodeRole.DynamicRole dynamicRole = new DiscoveryNodeRole.DynamicRole(
+                buildInRole.roleName(),
+                buildInRole.roleNameAbbreviation(),
+                buildInRole.canContainData()
+            );
+            assertNotEquals(buildInRole, dynamicRole);
+            assertNotEquals(buildInRole.toString(), dynamicRole.toString());
+            assertNotEquals(unknownDataRole, dynamicRole);
+            assertNotEquals(unknownDataRole.toString(), dynamicRole.toString());
         }
     }